1. Technical Field
The present invention relates to a glass lathe. In particular, the present invention relates to a glass lathe for heating and processing a glass member such as an optical fiber preform.
2. Related Art
A glass lathe is an apparatus for heating a rotating glass member such as a glass rod or glass tube with a burner flame, in order to perform processing such as welding, fusion cutting, drawing, or fire polishing. The apparatus of the present invention is used when processing an optical fiber preform, for example. An oxyhydrogen flame is usually used by a glass lathe for processing a glass member. In particular, when the glass member is quartz glass, the temperature change can reach 2000° C.
In a glass lathe, when the glass member is heated, heat is added to the glass member from the burner flame as a result of convective heat transfer. Heat is released by being emitted from the heated glass member. The amount of heat emitted by the glass member is extremely large, because the temperature of the glass member reaches close to 2000° C. The amount of heat emitted from the glass member can be calculated according to the Stefan-Boltzmann Law. When the reflectivity is 1.0 and the surrounding temperature is 20° C., the energy loss due to emission per unit area is 1.5 MW/m2. For example, if the glass rod 2 is assumed to have a diameter of 80 mm and the heated region is assumed to have a length of 80 mm, the side surface area is approximately 20,000 mm2, and therefore the energy loss from the side surface is approximately 30 kW. In other words, in order to maintain a temperature of 2000° C., it is necessary to constantly apply 30 kW of heat to the glass rod 2. Therefore, the necessary flow rate of hydrogen gas is approximately 400 L/min, based on experience. Since the amount of heat generated when performing the firing with 400 L/min of hydrogen is 73 kW, the thermal efficiency is calculated to be approximately 41%.
Since the processing of the glass member consumes a large amount of energy in this way, lower energy consumption is desired when considering the environmental burden and cost. Patent Document 1 discloses a method of surrounding the portion of the glass member being heated with a surrounding body made of high-purity quartz. The temperature of this surrounding body is an intermediate temperature between room temperature and the temperature of the glass member, and therefore the heat emitted from the surrounding body to the room is less than the temperature emitted directly from the glass member. Furthermore, the heat generated by the firing is more efficiently transferred to the glass member.
Patent Document 1: Japanese Translation of PCT International Application No. 2009-508789
In the method of Patent Document 1, the quartz material of the surrounding body functions only as a heat insulator and a heat storage tank. Accordingly, a large amount of heat emitted from the glass rod 2 is lost, and the heating efficiency is decreased. Furthermore, with the method of Patent Document 1, when the surrounding body is used to heat the glass member, glass evaporates from the surface of the glass member. The evaporated glass is deposited as soot on the inner surface of the surrounding body at a lower temperature, and the deposited soot falls away and becomes attached to the glass member, thereby reducing the quality of the glass member. Furthermore, if the temperature is lowered after the processing and processing is then performed again, a large amount of the glass soot deposited on the inner surface of the surrounding body falls away and sticks to the glass rod. In order to avoid this problem, a cooling and cleaning process must be performed before the subsequent processing, and this lowers the capacity utilization rate.
In consideration of the above problems, it is an object of the present invention to provide a glass lathe that can increase heating efficiency when heating a glass member using a burner flame. The glass lathe preferably restricts the glass member from being contaminated with soot or the like.